I've been here a long time but more on the reader side, today a decided to share the new portable speaker I've been working.

First, this probably the 5th portable speaker I've built, so its a culmination of everything I've learned on previous build plus a few bookshelf and sub-woofers.

The drivers will be the same as my previous box, two 4,5" Eastech mid bass and two Peerless DQ25SC16. No wait, 4 of each, since I will build two almost identical boxes, one for me and one for my father.

This is what I wanted:
-Smaller than the previous one (10l max vs 21l)
-Play way lower

This mid bass was something golden that I found on a electronic stores, bought it what parameters whatsoever. After measuring I knew it would perform well

Bellow is an simulation in Hornresp of what I came up. Extension to almost 40 Hz in a 3,5 l enclosure. The way to do that was tunning the passive radiator really low as a mean to keep excursion under control, and them just brute force trough equalization.

Response @ 2pi

In theory it would work, but I wasn't so sure, so I build a test box to measure and more important, listen. My biggest worry is that the high excursion even at low volumes would distort the rest of the spectrum

It worked perfectly, I used my Mini DSP to apply the required equalization and took a quick measurement to see what the response looked like, and after that hooked up a tweeter just to listen for a few hours and see if the sound was pleasing.

Near field response of each driver and summed response

After that what was left to do was finish the box design and design a filter to go with it

For the box I went with the smallest size that could fit the drivers, the final dimensions is 401x148x183mm, all made to be CNC cut

For the filter I have a PEQ, a 4th order butterworth low pass and a BSC, all adjustable from outside the box by just removing the back portion of the cloth. The PCB should arrive soon

Today I received all CNC cut wood, my plan is to assemble the box this week and take some measurements to start working on the crossover

Very impressive build!
Do you have any information about the midbasses? Part number and so on?
I assume you know from experience what is required from your filter PCB if you dare to order it before measuring the box

The part number is FSB527550-5B24. Unfortunately the 8 ohms versions is long gone and the 12 ohms was available until recently but I went to check and it's also gone. I bought them 5 years ago

About the filter, after I modeled the required filter and tested on the test box with the MiniDSP I am pretty confident that it will work, bellow is the expected filter response. Red with just the PEQ, blue PEQ + High pass and purple PEQ + High Pass + BSC

Hopefully it will, the drawback is that the overall level is reduced a lot in order to keep under the excursion limits, but I don't need it to be super loud. The previous version used 4 of these drivers, but I can count on one hand how many times I used them to the full potential

After another round of measurements I have a crossover, i may tweak it a bit

I'm not sure about the Dz of the tweeter, following Troels methodology (Time-Alignment) I arrived at 33mm and adjusted the crossover accordingly, but them I can't get a deep notch at the response anymore, I guess that's the price for not having the drivers acoustically aligned

I am onto this as well, see if you can source Monacor SP-60 - these have very low Fs, suitable for sealed and 90db/w (and are cheap ). They require a large box, so small sealed with active help should work. Just an idea.

Why would you go for passive crossovers and not active ones (smaller, cheaper, can boost bass output, lighter)? Something like a TPA3255 I believe can do the job and run quite long on batteries?

At this point I kinda wished that I went full active, the PCB would be a bit more complex but nothing I can't manage. The amp for the tweeter can be cheap, 10W would be more than enough since it's way more sensitive

I will simulated an active crossover and see what it looks like

Also the PCB's arrived a few days ago, they look beautiful and very high quality, for the price it's a steal